The present invention relates to a novel radiation curable or crosslinkable organopolysiloxane compound or, more particularly, to a novel radiation-curable or crosslinkable organopolysiloxane compound which is suitable to form a cured surface film on a substrate surface having releasability against adhesives or sticky substances and useful as a back-surface treatment agent of pressure-sensitive adhesive tapes or surface treatment agent of release paper for pressure-sensitive adhesive labels and the like, hereinafter referred to as a surface-releasing agent, as well as to a method for the preparation of such a novel organopolysiloxane compound.
The invention also relates to a method for forming a surface-releasing film on the surface of a substrate by using the organopolysiloxane compound.
It is well known that a variety of organopolysiloxanes or compositions thereof are used in the application as a surface-releasing agent, of which organopolysiloxanes having two or more of (meth)acryloxy, i.e. acryloxy or methacryloxy, groups in a molecule are widely used as a radiationcurable surface-releasing agent by virtue of their crosslinkability by the irradiation with electron beams.
Such a (meth)acryloxy-containing organopolysiloxane has a problem that the surface-releasability against adhesive materials is necessarily decreased when the density of the (meth)acryloxy groups therein is increased with an object to obtain improved radiation-crosslinkability. This disadvantage can be partly overcome by admixing the (meth)acryloxycontaining organopolysiloxane with a dimethylpolysiloxane of a straightly linear molecular structure having a high molecular weight but no radiation-crosslinkability (see, for example, Japanese Patent Kokai No. 62-30234). Though not ineffective in improving the surface releasability, such an organopolysiloxane composition has a problem that the coating film produced by the electron beam irradiation of low dose is poor in respect of the residual adhesiveness. Alternatively, a proposal has been made in Japanese Patent Kokai No. 62-11914 for the use of an organopolysiloxane having (meth)acryloxy groups bonded only to the silicon atoms at the molecular chain ends as a coating agent of optical fibers. Such an organopolysiloxane, however, is not quite satisfactory as a surface-releasing agent due to the relatively poor releasability characteristics when a coating film thereof is cured by the irradiation with radiations.